3
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What is the minimum number of 1/4 turns of a solved 2x2 Rubik’s cube, such that no face will have two tiles of the same color?

(I do not have this puzzle’s solution.)

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3
  • $\begingroup$ Is this an original puzzle? $\endgroup$
    – bobble
    May 6 at 3:05
  • $\begingroup$ @bobble It is, as far as I know. However, it does seem like the sort of thing someone else may have asked in the past, doesn’t it? $\endgroup$
    – Gilbert
    May 6 at 3:19
  • $\begingroup$ "As far as I know" is good enough for here :) The attribution requirement is meant to catch people who copy-paste from another source, or similar. $\endgroup$
    – bobble
    May 6 at 3:25
5
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This is the shortest sequence I found:

It can be done in 5 moves.
Using standard notation, the moves are: RDRDF.
Here is a graphical rundown of the moves: enter image description
 here

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  • $\begingroup$ Do you have a proof for why less moves is impossible? $\endgroup$
    – bobble
    May 7 at 0:05
  • $\begingroup$ It’s been 24 hours, so I’m calling this solved (although I reserve the right to reconsider if someone comes along with a proof!). Great job! Also, thank you for the graphical rundown; I’m not fluent in the notation. $\endgroup$
    – Gilbert
    May 7 at 4:07
  • $\begingroup$ I went through all the non-equivalent 4-length sequences as best I can, and none of them works. But I'm not 100% sure I got them all, and it's not a very elegant proof $\endgroup$
    – Joe
    May 7 at 4:24

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